In U.S. Pat. Nos. 4,293,400, 4,378,276 and 4,872,959 there are described devices for applying an electric field to a liquid which flows between electrodes incorporated in the devices. In these devices, the electrodes are metal tubes or pipes whose sizes are predetermined by the sizes of pipe which is commercially available. It will be appreciated that the spacing between the electrodes is critical in order to optimize the treatment process, but since the electrode diameter is dictated by the pipe sizes which are available, optimum spacing cannot always be provided economically because of the increased cost of special pipe sizes and the need to use non-standard fittings. For example, the cost of a non-standard pipe assembly is commonly five times the cost of an assembly using off-the shelf pipes and fittings.
Another problem with the devices described in the referent patents is the difficulty and expense in precisely spacing the tubular electrodes from one another throughout the length of the device. If the spacing is less at one or more locations along the electrodes, more current will be conducted through the liquid at those locations resulting in a greater sacrifice in the pipe metal at those locations than at other places along the electrodes. Consequently, pipe life is decreased, and in addition, the efficiency of the process is reduced since the liquid will be primarily treated at the locations where the electrode spacing is least rather then throughout the overall length of the device. This makes the percentages of removed impurities per pipe less and the amount of impurities removed for a given amount of power less. In fact, any appreciable variation in the spacing between the electrodes dramatically increases the cost per gallon of treating the liquid.
The electrolytic devices described in the referent patents provide a helical flow path between the tubular electrodes which allows more metal surface contact between the liquid and the electrodes and optimizes the dwell time and processing surface area of the electrodes. However, the helical flow path has the disadvantage of increasing the flow resistance and the necessary operating pressure of the system resulting in an increased operating cost and the need for more expensive pumps and fittings to withstand the higher operating pressures.
Another disadvantage of the prior art tubular electrode systems is one of maintenance because disassembly requires that the pipes be unscrewed which is made difficult when corrosion has occurred. Also, since sacrificing does not always occur uniformly, it is sometimes very difficult to withdraw the inner electrodes from the outer electrodes.
In order to increase the capacity of the treatment devices which use tubular electrodes, attempts have been made to use larger diameter electrodes, but this has proven to be uneconomical because the added cost of the electrodes more than offsets the benefits provided by the increased volume.